Implantable cardiac defibrillator (ICD) systems are used to delivery high energy electrical pulses or shocks to a patient's heart to terminate life-threatening arrhythmias, such as ventricular fibrillation. Traditional ICD systems include an ICD device and one or more implantable medical electrical leads connected thereto; the device, which has a hermitically sealed housing that encloses a pulse generator and other electronics thereof, is implanted subcutaneously in the chest of the patient, and the leads, referred to herein as transvenous leads, are implanted within the heart.
Traditional ICD systems that utilize transvenous leads may not be preferred for all patients, such as those in whom difficult vascular access precludes the placement of transvenous leads. Moreover, transvenous leads may become fibrosed in the heart over time, making lead revision and extraction procedures challenging. Thus, for some patients, an extravascular ICD system may be preferred, in which a lead (or leads) are implanted in an extravascular location, that is, outside the vascular system of the patient, rather than within the vascular system, for example, in a subcutaneous, sub-sternal, or other extravascular location.